The aim of this study was to investigate effect of different sources of ration's fat with or without stress condition on metabolism in mature rams. 12 adult Afshari rams with an average initial weight of 64.58 Kg were used. The rams were distributed randomly among the four treatments: 1: diet containing 4% soybean oil. 2, diet containing 8% full-fat soybean. 3, diet containing 4% calcified soybean oil. 4, diet containing 4% tallow. Rations were adjusted according to the rams’ maintenances need. Three months after beginning of experiment, the stress condition was performed based on hourly injection of 0.1 mg per kg body weight for 48 hours. Blood samples were taken from the jugular vein of all animal before and after stress. The serum concentration of testosterone, cortisol, cholesterol, LDL, HDL, VLDL, glucose, TG, albumin, globulin, albumin/globulin, total protein, were measured. Body weight change evaluated before and after induction of stress. The result indicated a significant (P 0.05) decrease in testosterone concentrations after stress induction. Testosterone levels were significantly (P 0.05) higher in calcified soybean oil treatment compared to other treatments. Cortisol concentration significantly (P 0.05) increased in stress condition. There was a significant (P 0.05) increase in cortisol concentrations for diet containing 4% soybean oil. Cholesterol concentrations were lower in full fat soybean treatment than those soybean oil and calcified soybean oil treatments after stress induction. There was significant (P 0.05) increase in cholesterol concentrations in stress condition. The concentration of blood LDL were significantly (P 0.05) decreased in treatment 4 than those treatments 1 and 3. But stress effect was not significant (P 0.05) on the LDL concentration. HDL levels significantly (P 0.05) increased in the condition of stress. The highest concentration of HDL was related to diet containing 4% soybean oil. There were no significant (P 0.05) differences in the concentrations VLDL in stress condition. The lowest concentration of VLDL was observed in full-fat soybean treatment at stress condition. Triglyceride concentrations were not affected by treatments and stress condition (P 0.05). Intraction of treatments and stress were significant (P 0.05) on the triglyceride levels. Diet containing calcified soybean oil had higher triglyceride levels in stress condition. Total protein concentrations were not influenced by stress and treatments. Stress affect the immune system and significantly (P 0.05) reduced serum globulin. The lowest concentration of albumin and highest globulin concentrations were observed in diet containing tallow. Albumin to globulin ratio had significant (P 0.05) difference in diet containing tallow compared to others treatments. Intraction of stress and treatment was not significant (P 0.05) on this ratio. The result showed a significant (P 0.05) increase in glucose concentration in stress condition. The effect of stress on glucose concentration was significant (P 0.05). Stress and sources of added fat to diet and also intraction of stress and treatments did not affect the body weight of rams (P 0.05). Our results showed tallow had benefit effect in blood metabolites of rams in stress conition. Keywords: Stress, Fat, Testosterone, Parameters of Blood, Ram.